Wear resistant steels are currently used in equipment or parts used in industrial sectors such as construction, transportation, mining, and railway engineering requiring wear resistant characteristics.
Wear resistant steels are broadly categorized as austenitic work hardened steels and high hardness martensitic steels.
A representative example of an austenitic work hardened steel is a Hadfield steel which has been used for about 100 years. Hadfield steel includes about 12% of manganese (Mn) and about 1% of carbon (C), wherein the microstructure thereof includes austenite, and Hadfield steel is in use in various sectors such as the mining industry, in railway engineering, and in the defense sector. However, since the initial yield strength thereof is relatively low at about 400 MPa, the use thereof as a general wear resistant steel or structural steel is limited.
In contrast, since high hardness martensitic steels have high yield strength and tensile strength, the high hardness martensitic steels are being widely used in structural materials and transportation/construction equipment. In general, a high hardness steel includes high amounts of carbon and high amounts of alloying elements, and a quenching process is essential for securing a martensitic structure capable of providing sufficient strength. Typical martensitic wear resistant steels include HARDOX series steels by SSAB AB, in which both strength and hardness are excellent.
There are many cases in which wear resistant steels having high resistance to abrasive wear are required according to the use environment thereof, and the hardness of a surface portion of such steels is very important to secure resistance to abrasive wear therein. Typically, large amounts of alloying elements are added to obtain high hardness of the surface portion, and the wear resistant steels for abrasive wear resistance contain a large amount of carbon having a large effect on the hardness of the surface portion. However, when the large amount of carbon is contained, cracks may easily occur in welding zone during welding. Also, when the thickness of a product increases, it may be difficult to obtain high hardness in to the center thereof. Thus, a large amount of a hardening element, such as chromium (Cr) or molybdenum (Mo), is added to compensate for this. However, since an expensive hardening element must be added, manufacturing costs may increase. In addition, relatively expensive nickel (Ni) may also be added to improve impact characteristics of a product. However, the required amount of Ni increases when the thickness of the product increases. Thus, it may be uneconomical.